Method of calibrating an ophthalmic-lens-piercing machine, device used to implement one such method and ophthalmic-lens-machining apparatus comprising one such device

ABSTRACT

The invention relates to a method of calibrating an ophthalmic-lens-piercing machine, a device used to implement one such method and an ophthalmic-lens-machining apparatus comprising one such device. The inventive method applies to a machine comprising a piercing tool, a lens support which is associated with a first reference mark (O 1 , X 1 , Y 1 ), and programmable tool-control means which are associated with a second reference mark expressing set co-ordinates which define a target piercing point (M). The inventive method consists in: placing a template ( 21 ) on the support, said template comprising pre-applied markings defining a third reference mark (O 3 , X 3 , Y 3 ), such that the third reference mark is essentially in line with the first reference mark; piercing the template at a pre-determined point corresponding to a target point; taking an image of the template thus pierced; analysing said image such as to measure the misalignment between the real piercing point position and the target point position; and programming the control means, such as to apply a correction to the set co-ordinates that can compensate for the misalignment. The invention also relates to a device which is used to implement said method and to an ophthalmic-lens-machining apparatus comprising one such device.

The present invention relates to a method for calibrating an ophthalmic lens drilling machine, the said machine comprising:

a drilling tool;

an ophthalmic lens support associated with a first coordinate system; and

programmable tool guidance means which are associated with a second coordinate system expressing command coordinates which define a target drilling point,

in which method the following successive steps are carried out:

a template is placed on the support, the template having pre-applied markings defining a third coordinate system related to the said template, such that the third coordinate system is made to substantially coincide with the first coordinate system; and

the template is drilled in at least one predetermined point corresponding to a target point defined by predetermined command coordinates, such that a real drilling point is obtained.

FIG. 1 shows schematically an ophthalmic lens drilling machine of a known type, which essentially comprises a support 2 on which a lens can be mounted and fixed for grinding, a drilling tool 3 which can be moved in a controlled way with respect to the support 2, and means 11 for guiding the tool 3.

The support 2 is shown schematically in the form of a receptacle enabling ophthalmic lenses of different shapes to be fixed with respect to the frame, in a fixed coordinate system O₁, X₁, Y₁ associated with the support 2. The support 2 is provided to hold the ophthalmic lens in a support plane which is assumed to be horizontal. The reference axes X₁, Y₁ are therefore assumed to be horizontal.

The support 2 which is shown is a receptacle having an internal shape complementary to that of an adapter, of the type conventionally used to fix the lens on the movable arm of a grinder. An adapter of this kind is fixed, by gluing for example, to one of the faces of the lens. The receptacle 2, which is intended to receive an adapter of this type by insertion, has an indexing shape 2A complementary to an indexing shape of the adapter, which enables the lens to be orientated on the support 2, and thus with respect to the frame of the machine 1. The indexing means 2A thus define the orientation of the support 2 and of the frame of the machine, in other words the coordinate system O₁, X₁, Y₁.

The drilling tool 3 is defined as being a tool which removes material around an axis, assumed in this case to be vertical (orthogonal to the axes X₁, Y₁), in the thickness of the lens, over a virtually point-like region of the lens or one having an area much smaller than the area of the lens. The term “drilling” can denote a conventional operation of drilling with a drill bit, resulting in the formation of a hole with a substantially circular cross section, or else an operation of “notching”, resulting in the formation of a notch in the edge of the lens, or any other type of more complex milling.

The means 11 for guiding the tool 3 are provided to move the tool 3 according to a machining task to be carried out on a lens placed in the machine. For this purpose, these guidance means 11 comprise drive means 13 adapted to move the tool 3, and means 15 for controlling the drive means 13, adapted to deliver to the drive means 13 a command signal C corresponding to the machining task to be performed. The control means 15 are programmable means: they are provided to store a certain number of control laws with parameters set according to the shape and position of the drilling to be carried out. Thus the sequence of movements and operations executed by the tool 3, defined by the command signal C, is a function of the shape and position parameters supplied to the input of the control means 15. These parameters are indicated in FIG. 1 by the reference F (shape parameters) and by the references X, Y (position parameters). The position parameters X, Y are expressed in the second frame reference associated with the control means 11, this virtual coordinate system theoretically coinciding with the first coordinate system O₁, X₁, Y₁ related to the support 2.

FIG. 2 shows an ophthalmic lens 21 of generally rectangular shape, having a centre marking 03 and axis markings X₃, Y₃ on one of its faces.

The centre O₃ represents the optical centre of the lens 21, and the axis X₃ represents its optical axis. The purpose of the marking of the axis Y₃, perpendicular to the axis X₃ in the general plane of the lens 21, is essentially to define the optical centre O₃ at its intersection with the axis X₃.

When an adapter is centred on an ophthalmic lens blank for grinding, the centre of the adapter coincides with the optical centre O₃ of the blank.

Thus, after the grinding operation which results in the production of the lens 21 in its finished form, when the lens 21 with its grinding adapter is placed on the support 2 for drilling in the machine 1, the centre of the support 01 theoretically coincides with the optical centre O₃ located by the axis markings X₃, Y₃ on the leans 21.

If a hole is then to be drilled in the lens 21 with the drilling machine 1, the position parameters X, Y and the shape parameter F must be supplied to the control means 15, as mentioned above. For example, in order to create a virtually point-like circular drilled hole, the position parameters X, Y consist of the coordinates of the centre M of the drilled hole. The coordinates X, Y, which are expressed in the second coordinate system associated with the guidance means 11, theoretically represent the coordinates of the centre of drilling M in the coordinate system related to the lens, in other words the third coordinate system O₃, X₃, Y₃.

When the drilling is actually carried out, it will be found that the real centre of drilling (or real drilling point) M_(r) is offset with respect to the theoretical centre of drilling (or target drilling point) M, as defined by the coordinates X, Y in the third coordinate system O₃, X₃, Y₃.

This situation is shown in FIG. 3, in which the profile of the lens 21 and its markings defining the coordinate system O₃, X₃, Y₃ are shown in solid lines, and the indexing shape 2A and the associated coordinate system O₁, X₁, Y₁, as positioned with respect to the lens 21 when the latter is placed in the drilling machine 1 on the support 2, are shown in broken lines. The real centre of drilling M_(r) is also shown on the lens 21 in solid lines, and the theoretical centre of drilling M is shown in broken lines.

For reasons explained below, this offset is expressed by the coordinates dX, dY in one of the three pre-defined coordinate systems, which is assumed to be any one of these coordinate systems.

As a general rule, the offset of the real drilling points with respect to the theoretical drilling points is explained by the fact that the three coordinate systems defined above do not coincide exactly:

on the one hand, the second coordinate system, associated with the guidance means 11 and taken as the reference, for example, of the neutral position of the tool 3, is not exactly locked to the first coordinate system O₁, X₁, Y₁ related to the support 2. This is due to the manufacturing tolerances and to the wear of the mechanical components used in the adjustment of the neutral position of the tool, to the tolerances and wear of the mechanical components of the drive means 13, and to the intrinsic inaccuracies of the control elements used in the feedback control of the position of the tool 3, for example; and

on the other hand, the third coordinate system O₃, X₃, Y₃ related to the lens 21 does not coincide exactly with the first coordinate system O₁, X₁, Y₁ related to the support 2. This is due, in particular, to the inaccuracy, even if very small, of the positioning of the adapter on the lens, and the inaccuracy of the fixing of the adapter to the said support 2, resulting, for example, from the manufacturing tolerances of these parts and from the possible deformation of the adapter during the preliminary grinding operation.

It should be noted that the offsets generally found in drilling machines between the theoretical and the real drilling points tend to indicate that there is no significant angular offset between the different coordinate systems. Consequently, in the description of the present invention, it is assumed that these coordinate systems are offset only with respect to translation, and that their horizontal axes, on the one hand, and their vertical axes, on the other hand, are parallel. This has been illustrated in FIG. 3, between the first coordinate system O₁, X₁, Y₁ and the third coordinate system O₃, X₃, Y₃.

For drilling machines used at present, it is therefore necessary, before the first use of the machine, to estimate the offset between the real drilling points and the theoretical drilling points, and to calibrate the machine so as to introduce a correction of the control laws into the control means 15. These calibration operations can be renewed periodically thereafter throughout the service life of the machine.

The correction which is introduced takes the form of a change of variables; for example, the position parameters taken into account for the calculation of the command C are X+dX, Y+dY, in place of the input parameters X, Y.

In the prior art, these calibration methods are implemented on the basis of a “manual” measurement of the offset produced by the uncalibrated machine. In the prior art, an operator uses the uncalibrated machine to drill a succession of virtually point-like circular holes in a template, such as an ophthalmic lens, and measures the positions of these drilled holes on the template by means of a caliper gauge. The operator then deduces the offset of each drilled hole with respect to the theoretical drilling points, and introduces a corresponding correction into the programmable machine guidance means. This correction can, for example, take into account a mean of the offsets found over all the measurement points.

This method has two principal drawbacks, namely the low accuracy of the measurement of the offset (of the order of a 10th of a millimetre), and the considerable time taken for the operation.

The object of the invention is to propose a calibration method of the type described above, making it possible to obtain a marked increase in accuracy, and requiring a shorter operating time and markedly simpler manipulation operations. This object is achieved by a calibration method according to the invention, in which the following steps are executed in succession:

an image of the previously drilled template is created;

the said image is analysed by image analysis means, so as to measure the offset between the position of the real drilling point and the position of the target point; and

the guidance means are programmed so as to introduce a correction of the command coordinates capable of compensating for the said offset.

According to other characteristics of this method:

the markings defining the third coordinate system comprise markings which define a centre and markings which define two orthogonal axes; and

during the drilling step, the template is drilled at two predetermined points, each corresponding to a target point defined by predetermined command coordinates, so as to obtain two real drilling points, and the correction is based on a mean value of the offset of the position of the two real drilling points with respect to the respective two target points.

The invention also proposes a device for implementing a calibration method as described above, this device comprising:

an image capture device;

image analysis means connected to the said image capture device, adapted to detect the position of the image of a real drilling point of a template, in a coordinate system defined by the image of markings appearing on the said template, and to calculate an offset of position of the said image with respect to a predetermined target point defined by pre-recorded coordinates; and

programming means connected on the one hand to the image analysis means and on the other hand to the means for guiding an ophthalmic lens drilling machine, the said programming means being adapted to receive an offset information element from the image analysis means, and to program the guidance means of the machine in response, so as to introduce a correction of the command coordinates as a function of the said offset information.

According to other characteristics of the device according to the invention:

the device additionally comprises a screen and means for illuminating an ophthalmic object, enabling a shadow of the template to be projected on to the screen, the said screen being placed in the field of observation of the said image capture device;

the device comprises a transparent support to receive the template, positioned between the means of illumination and the screen;

the device comprises a collimator positioned between the means of illumination and the transparent support to make the light rays emitted by the means of illumination substantially parallel to each other and normal with respect to the support;

the screen is a ground glass; and

the image capture device is a video camera.

Finally, the invention proposes equipment for machining ophthalmic lenses, comprising:

a drilling machine which has a drilling tool, an ophthalmic lens support associated with a first coordinate system, and programmable means for guiding the tool, associated with a second coordinate system in which command coordinates defining a target drilling point are expressed, and

a device as described above, associated with the said drilling machine.

A specific embodiment of the invention will now be described more fully with reference to FIGS. 4 and 5 of the attached drawings, in which:

FIG. 4 is a schematic view of a device according to the invention; and

FIG. 5 is a partial view of the image of a template, as it may be observed by the image capture device of the device according to the invention.

In the calibration method according to the invention, a template is drilled by means of the uncalibrated machine 1, shown in FIG. 1, as explained previously. In the illustrated example, this template consists of an ophthalmic lens 21, as described with reference to FIG. 2, but could be another ophthalmic object such as a template of plastics or other material, provided with centre and axis markings.

The adapter of the template 21 is removed, and the template is then cleaned to remove any trace of adhesive originating from the adapter from the surface of the template, and to leave the markings associated with the coordinate system O₃, X₃, Y₃ visible on the surface of the template.

The coordinates dX, dY of the offset between the real drilling points M_(r) and theoretical drilling points M are then estimated by the device 51 shown in FIG. 4.

This device 51 comprises a flat transparent support 53 on which can be placed the drilled template 21, which has previously been separated from its adapter.

It also comprises a light source 55, a collimator 57, and a ground glass 59, positioned in such a way that the light rays emitted by the source 55 pass through the collimator 57 to be made parallel and orthogonally illuminate the template 21 placed on the support 53. This arrangement enables the drilled template and its markings O₃, X₃, Y₃ to be projected on to the ground glass 59.

The device additionally comprises an image capture device in the form of a video camera 61, image analysis means 63 connected to the camera 61, and if necessary a display screen 65 connected to the image analysis means 63. The screen 65 could also be connected directly to the camera 61.

The ground glass 59, forming a screen for the projection of the shadow of the object placed on the support 53, is placed in the field of the camera 61, in such a way that the camera 61 observes this projected shadow and transmits its image to the image analysis means 63.

The device also comprises programming means 64 connected, on the one hand, to the image analysis means 63, and, on the other hand, to the means 11 for guiding the machine 1.

FIG. 5 shows the image 21I of the template 21 which is thus observed by the camera 61, as it appears on the screen 65.

The shadow of the drilled hole IM_(r), and the shadows of the centre marking IO₃ and of the axis markings IX₃, IY₃ appear distinctly in this image 21I.

The image analysis means 63 are adapted to:

detect the image IM_(r) of the drilled hole formed in the template 21, and the image of the markings IO₃, IX₃, IY₃,

calculate the position of the drilling point IM_(r) in this image coordinate system IO₃, IX₃, IY₃, and

calculate in this coordinate system the coordinates of the offset dX, dY between the point M_(r) and the point M, which are assumed to be equal to the difference between the coordinates of the point IM_(r) in the coordinate system IO₃, IX₃, IY₃, on the one hand, and those of the point M in the second coordinate system.

The value of the offset dX, dY estimated in this way is transmitted to the programming means 64.

If necessary, the offset can be measured for two or more distinct drilling points, rather than for a single point as described above. The correction of the control laws can then be based on a mean of the offsets estimated in this way.

Thus the device 51 makes it possible to produce a precise estimate of the offset of a real drilling point with respect to a target point, and, because of its programming means 64, to automatically program the guidance means 15 of the ophthalmic lens drilling machine so as to introduce a correction of the command laws dependent on the estimated offset coordinates dX, dY. The accuracy achieved by such a device and such a calibration method is of the order of a hundredth of a millimetre.

It should be noted that the drilling machine 1 and the associated device which have been described can be incorporated into ophthalmic lens machining equipment which also comprises a grinder. Thus it is possible to use a single piece of equipment to grind an ophthalmic lens, starting with a lens blank, and to drill the lens thus produced, by using the grinding adapter fixed on the lens to immobilize the lens on the drilling support.

The device described above can be used for calibrating not only the drilling machine, but also the grinder. 

1. Method of calibrating an ophthalmic lens drilling machine, the said machine comprising: a drilling tool; an ophthalmic lens support associated with a first coordinate system; and programmable means for guiding the tool, which are associated with a second coordinate system expressing command coordinates which define a target drilling point, in which method the following successive steps are carried out: a template is placed on the support, the template having pre-applied markings defining a third coordinate system related to the said template, such that the third coordinate system is made to substantially coincide with the first coordinate system; and the template is drilled in at least one pre-determined point corresponding to a target point defined by predetermined command coordinates, such that a real drilling point is obtained, this method being characterized in that the following steps are then carried out in succession: an image of the template drilled in this way is created; the said image is analysed by image analysis means, so as to measure the offset between the position of the real drilling point and the position of the target pointy; and the guidance means are programmed so as to introduce a correction of the command coordinates capable of compensating for the said offset.
 2. Method according to claim 1, characterized in that the markings defining the third coordinate system comprise markings which define a centre and markings which define two orthogonal axes.
 3. Method according to claim 1, characterized in that, during the drilling step, the template His drilled at two predetermined points, each corresponding to a target point defined by predetermined command coordinates, so as to obtain two real drilling points, and the correction is based on a mean value of the offset of the position of the two real drilling points with respect to the respective two target points.
 4. Device for the implementation of a method according to claim 1, comprising: an image capture device; image analysis means connected to the said image capture device, adapted to detect the position of the image of a real drilling point of a template, in a coordinate system defined by the image of markings appearing on the said template, and to calculate an offset of position of the said image with respect to a predetermined target point defined by pre-recorded coordinates; and programming means connected on the one hand to the image analysis means and on the other hand to the means of guiding an ophthalmic lens drilling machine, the said programming means being adapted to receive an offset information element from the image analysis means, and to program the guidance means of the machine in response, so as to introduce a correction of the command coordinates as a function of the said offset information.
 5. Device according to claim 4, characterized in that it additionally comprises a screen and means for illuminating an ophthalmic object, enabling a shadow of the template to be projected on to the screen, the said screen (being placed in the field of observation of the said image capture device.
 6. Device according to claim 5, characterized in that it comprises a transparent support to receive the template, positioned between the means of illumination and the screens.
 7. Device according to claim 6, characterized in that it comprises a collimator positioned between the means of illumination and the transparent support to make the light rays emitted by the means of illumination 3 substantially parallel to each other and normal with respect to the support.
 8. Device according to claim 5, characterized in that the screen is a ground glass.
 9. Device according to claim 4, characterized in that the image capture device is a video camera.
 10. Equipment for machining ophthalmic lenses, comprising: a drilling machine which has a drilling tool; an ophthalmic lens support associated with a first coordinate system; and programmable means for guiding the tools, which are associated with a second coordinate system expressing command coordinates which define a target drilling point, and a device according to claim 4, associated with the said drilling machines. 